Posted by *Morris Dovey* on January 7, 2007, 7:06 pm

I decided to take a shot at writing a simple program to predict the

output of a south-facing vertical flat heating panel.

The starting point was the NREL web site; and I've collected the

applicable US maps on a web page at

http://www.iedu.com/DeSoto/SolarEnergy.html - so that people can get a

quick kWh/m^2/day value to plug into the program. Be warned that there

are 12 monthly maps of the USA and that the page may take a while to

download.

According to what I've been able to find on the web, flat panels can

get an input boost from snow reflection that increases energy input

anywhere from 35 to 95 percent, depending on age of snow, surface

texture, etc. and the program allows entering a "snow boost"

percentage. People living in areas without snow should probably enter

a very small number to account for local reflective effects.

Panel area (in square feet) is, of course, an important input.

The program asks for a panel efficiency percentage - and this will

probably be a dealer-supplied number, a measured value, or a wild

guess (or perhaps a design target).

The program outputs a single value: the number of Btus that a panel

matching the supplied parameters can be expected to deliver.

I'm posting the code here to find out if I've made any glaring

errors - and to solicit refinements...

GW-BASIC code follows:

100 INPUT "Panel area in ft^2";AREA

110 INPUT "Panel efficiency (%)";EFFICIENCY

120 INPUT "Increased input from snow reflection (%)";SNOWBOOST

130 INPUT "Average daily sun in kWh/m2 from NREL map";KWHPERM2

140 BTUPERFT2 = KWHPERM2 * 316.998331#

150 BTUS = AREA * BTUPERFT2

160 BTUS = BTUS * (100 + SNOWBOOST) / 100

170 BTUS = BTUS * EFFICIENCY / 100

180 PRINT "Panel delivers";BTUS;"Btu per day"

--

Morris Dovey

DeSoto Solar

DeSoto, Iowa USA

http://www.iedu.com/DeSoto

Posted by *Duane C. Johnson* on January 8, 2007, 3:01 am

Hi Morris;

> I decided to take a shot at writing a simple

> program to predict the output of a south-facing

> vertical flat heating panel.

> The starting point was the NREL web site; and I've

> collected the applicable US maps on a web page at

> http://www.iedu.com/DeSoto/SolarEnergy.html - so

> that people can get a quick kWh/m^2/day value to

> plug into the program. Be warned that there are 12

> monthly maps of the USA and that the page may take

> a while to download.

> According to what I've been able to find on the

> web, flat panels can get an input boost from snow

> reflection that increases energy input anywhere

> from 35 to 95 percent, depending on age of snow,

> surface texture, etc. and the program allows

> entering a "snow boost" percentage. People living

> in areas without snow should probably enter a very

> small number to account for local reflective effects.

> Panel area (in square feet) is, of course, an

> important input.

> The program asks for a panel efficiency percentage -

> and this will probably be a dealer-supplied number,

> a measured value, or a wild guess (or perhaps a

> design target).

Or you could do a pretty good estimate using a

concept I call "Stasis Temperature". See a more

in depth explaination:

http://www.redrok.com/concept.htm#stasis

A fairly easy equation:

STASIS = 340 Degrees Rankine at the 0%

efficiency temperature rise.

AMBT = Ambient temperature of the panel.

OPPT = Operating temperature of the panel.

EFFICIENCY = (STASIS + AMBT - OPPT) / STASIS * 100

> The program outputs a single value: the number of

> Btus that a panel matching the supplied parameters

> can be expected to deliver.

>

> I'm posting the code here to find out if I've made

> any glaring errors - and to solicit refinements...

Looks good to me.

> GW-BASIC code follows:

> 100 INPUT "Panel area in ft^2";AREA

> 110 INPUT "Panel efficiency (%)";EFFICIENCY

> 120 INPUT "Increased input from snow reflection (%)";SNOWBOOST

> 130 INPUT "Average daily sun in kWh/m2 from NREL map";KWHPERM2

> 140 BTUPERFT2 = KWHPERM2 * 316.998331#

> 150 BTUS = AREA * BTUPERFT2

> 160 BTUS = BTUS * (100 + SNOWBOOST) / 100

> 170 BTUS = BTUS * EFFICIENCY / 100

> 180 PRINT "Panel delivers";BTUS;"Btu per day"

10 CLS:COLOR 10

20 PRINT "Program to Estimate Solar Thermal"

30 PRINT " Panel Performance Morris02.bas"

40 PRINT " Written by Morris Dovey"

50 PRINT " modified by Duane C. Johnson"

60 PRINT " 2006/01/07"

80 STASIS = 340 :REM Temperature rise of a flat plate

81 :REM thermal panel with 2 layers of

82 :REM transparent insulation running

83 :REM at 0% efficiency.

100 COLOR 14

110 INPUT " Panel area in ft^2 "; AREA

120 REM INPUT " Panel efficiency (%) "; EFFICIENCY

130 INPUT " Ambient temperature F "; AMBT

140 INPUT " Operating temperature F "; OPPT

150 EFFICIENCY = (STASIS + AMBT - OPPT) / STASIS * 100

160 INPUT "Increased input from snow reflection (%) ";SNOWBOOST

170 INPUT "Average daily sun in kWh/m2 from NREL map ";KWHPERM2

180 BTUPERFT2 = KWHPERM2 * 316.998331#

190 BTUS = AREA * BTUPERFT2

200 BTUS = BTUS * (100 + SNOWBOOST) / 100

210 BTUS = BTUS * EFFICIENCY / 100

220 COLOR 12

230 PRINT " Panel delivers Btu per day";BTUS

240 PRINT : GOTO 100

> --

> Morris Dovey

> DeSoto Solar

> DeSoto, Iowa USA

> http://www.iedu.com/DeSoto

Duane

--

Home of the $5 Solar Tracker Receiver

http://www.redrok.com/led3xassm.htm [*]

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Posted by *Jeff* on January 8, 2007, 6:22 am

Duane C. Johnson wrote:

*> Hi Morris;*

*> *

*> *

*> > I decided to take a shot at writing a simple*

*> > program to predict the output of a south-facing*

*> > vertical flat heating panel.*

*> *

*> > The starting point was the NREL web site; and I've*

*> > collected the applicable US maps on a web page at*

*> > http://www.iedu.com/DeSoto/SolarEnergy.html - so*

*> > that people can get a quick kWh/m^2/day value to*

*> > plug into the program. Be warned that there are 12*

*> > monthly maps of the USA and that the page may take*

*> > a while to download.*

*> *

*> > According to what I've been able to find on the*

*> > web, flat panels can get an input boost from snow*

*> > reflection that increases energy input anywhere*

*> > from 35 to 95 percent, depending on age of snow,*

*> > surface texture, etc. and the program allows*

*> > entering a "snow boost" percentage. People living*

*> > in areas without snow should probably enter a very*

*> > small number to account for local reflective effects.*

*> *

*> > Panel area (in square feet) is, of course, an*

*> > important input.*

*> *

*> > The program asks for a panel efficiency percentage -*

*> > and this will probably be a dealer-supplied number,*

*> > a measured value, or a wild guess (or perhaps a*

*> > design target).*

*> *

*> Or you could do a pretty good estimate using a*

*> concept I call "Stasis Temperature". See a more*

*> in depth explaination:*

*> http://www.redrok.com/concept.htm#stasis *

*> *

*> A fairly easy equation:*

*> STASIS = 340 Degrees Rankine at the 0%*

*> efficiency temperature rise.*

*> AMBT = Ambient temperature of the panel.*

*> OPPT = Operating temperature of the panel.*

*> EFFICIENCY = (STASIS + AMBT - OPPT) / STASIS * 100*

*> *

I was thinking along the same lines.

I notice that the equation that you have on RedRock has a solar

concentration factor. It seems to me that CF is really a proportion to

what the solar insolation is. This would then be very close to the

instantaneous efficiency which is roughly:

Solar Insolation / T operating - T ambient

Certainly the efficiency under lower light is much less. That would

imply that the actual snow boost is greater than calculated.

Just my 2 cents.

Jeff

*> > The program outputs a single value: the number of*

*> > Btus that a panel matching the supplied parameters*

*> > can be expected to deliver.*

*> >*

*> > I'm posting the code here to find out if I've made*

*> > any glaring errors - and to solicit refinements...*

*> *

*> Looks good to me.*

*> *

*> > GW-BASIC code follows:*

*> *

*> > 100 INPUT "Panel area in ft^2";AREA*

*> > 110 INPUT "Panel efficiency (%)";EFFICIENCY*

*> > 120 INPUT "Increased input from snow reflection (%)";SNOWBOOST*

*> > 130 INPUT "Average daily sun in kWh/m2 from NREL map";KWHPERM2*

*> > 140 BTUPERFT2 = KWHPERM2 * 316.998331#*

*> > 150 BTUS = AREA * BTUPERFT2*

*> > 160 BTUS = BTUS * (100 + SNOWBOOST) / 100*

*> > 170 BTUS = BTUS * EFFICIENCY / 100*

*> > 180 PRINT "Panel delivers";BTUS;"Btu per day"*

*> *

*> 10 CLS:COLOR 10*

*> 20 PRINT "Program to Estimate Solar Thermal"*

*> 30 PRINT " Panel Performance Morris02.bas"*

*> 40 PRINT " Written by Morris Dovey"*

*> 50 PRINT " modified by Duane C. Johnson"*

*> 60 PRINT " 2006/01/07"*

*> 80 STASIS = 340 :REM Temperature rise of a flat plate*

*> 81 :REM thermal panel with 2 layers of*

*> 82 :REM transparent insulation running*

*> 83 :REM at 0% efficiency.*

*> 100 COLOR 14*

*> 110 INPUT " Panel area in ft^2 "; AREA*

*> 120 REM INPUT " Panel efficiency (%) "; EFFICIENCY*

*> 130 INPUT " Ambient temperature F "; AMBT*

*> 140 INPUT " Operating temperature F "; OPPT*

*> 150 EFFICIENCY = (STASIS + AMBT - OPPT) / STASIS * 100*

*> 160 INPUT "Increased input from snow reflection (%) ";SNOWBOOST*

*> 170 INPUT "Average daily sun in kWh/m2 from NREL map ";KWHPERM2*

*> 180 BTUPERFT2 = KWHPERM2 * 316.998331#*

*> 190 BTUS = AREA * BTUPERFT2*

*> 200 BTUS = BTUS * (100 + SNOWBOOST) / 100*

*> 210 BTUS = BTUS * EFFICIENCY / 100*

*> 220 COLOR 12*

*> 230 PRINT " Panel delivers Btu per day";BTUS*

*> 240 PRINT : GOTO 100*

*> *

*> > --*

*> > Morris Dovey*

*> > DeSoto Solar*

*> > DeSoto, Iowa USA*

*> > http://www.iedu.com/DeSoto *

*> *

*> Duane*

*> *

Posted by *nicksanspam* on January 10, 2007, 1:28 pm

*>I decided to take a shot at writing a simple program to predict the*

*>output of a south-facing vertical flat heating panel.*

In BASIC :-)

*>The starting point was the NREL web site; and I've collected the*

*>applicable US maps on a web page at*

*>http://www.iedu.com/DeSoto/SolarEnergy.html - so that people can get a*

*>quick kWh/m^2/day value to plug into the program...*

It would be interesting to estimate the useful output of a solar heating

panel over a year from NREL's monthly average files for 239 stations. It

would be different for each month, and only useful if the average outdoor

temp were less than about 70 F.

*>According to what I've been able to find on the web, flat panels can*

*>get an input boost from snow reflection that increases energy input*

*>anywhere from 35 to 95 percent...*

... 95% is high. Page 238 of NREL's Blue Book says they use a ground

reflectance of 0.2. With a higher reflectance Rhog, we can add Iadj

= 0.5(Rhog-0.2)Ih(1-cos(beta)) to their published data, where Ih is

the global horizontal radiation and beta is the collector tilt.

Ih = 620 (Phila in Jan) and Beta = 90 degrees and Rhog = 0.6 (fresh snow)

makes Iadj = 0.5(0.6-0.2)620(1-0) = 124 Btu/ft^2 to add to the 1000 Btu/ft^2

of global sun on a south wall.

*>The program asks for a panel efficiency percentage - and this will*

*>probably be a dealer-supplied number, a measured value, or a wild*

*>guess (or perhaps a design target).*

I tend to think of 4'x8' air heater boxes as expensive undersized toys,

producing the heat equivalent of about 1 gallon of oil per square foot

per year, a lot less than the annual heat requirement for an average house.

And they have sides and insulation board on the back, a lot more stuff than

an 8'x32' south wall covered with $/ft^2 R1 Dynaglas "solar siding" with

90% solar transmission.

Knowing the outdoor temp, we can estimate the heat gain directly.

If 1000 Btu/ft^2 falls on a south wall over 6 hours (say 2 hours less

than the calculated day length) on an average January day in Phila when

the outdoor temp is 34 F and the average collector air temp is 100 F,

the net heat gain is 0.9x1000-6h(100-34)1ft^2/R1 = 504 Btu/ft^2 per day.

Nick

Posted by *nicksanspam* on January 10, 2007, 2:19 pm

*>... Page 238 of NREL's Blue Book says they use a ground reflectance of 0.2.*

Oops. That was page 248.

*>Knowing the outdoor temp, we can estimate the heat gain directly.*

*>If 1000 Btu/ft^2 falls on a south wall over 6 hours (say 2 hours less*

*>than the calculated day length)...*

And the number of daylight hours (equation 1.6.11 from my shiny new D&B)

is N = 2/15cos^-1(-tan(L)tan(D)), where L is the latitude and declination

D = 23.45sin(360(284+n)/365) and n is the day of the year.

Phila is about 40 n. lat, and D = -20.9 on an average January day,

so N = 2/15cos^-1(-tan(40)tan(-20.9)) = 9.5 hours, which agrees

with the nomogram on page 18. Maybe we should subtract 3 vs 2 hours

for the solar collection period.

Nick

> Hi Morris;>>> > I decided to take a shot at writing a simple> > program to predict the output of a south-facing> > vertical flat heating panel.>> > The starting point was the NREL web site; and I've> > collected the applicable US maps on a web page at> > http://www.iedu.com/DeSoto/SolarEnergy.html - so> > that people can get a quick kWh/m^2/day value to> > plug into the program. Be warned that there are 12> > monthly maps of the USA and that the page may take> > a while to download.>> > According to what I've been able to find on the> > web, flat panels can get an input boost from snow> > reflection that increases energy input anywhere> > from 35 to 95 percent, depending on age of snow,> > surface texture, etc. and the program allows> > entering a "snow boost" percentage. People living> > in areas without snow should probably enter a very> > small number to account for local reflective effects.>> > Panel area (in square feet) is, of course, an> > important input.>> > The program asks for a panel efficiency percentage -> > and this will probably be a dealer-supplied number,> > a measured value, or a wild guess (or perhaps a> > design target).>> Or you could do a pretty good estimate using a> concept I call "Stasis Temperature". See a more> in depth explaination:> http://www.redrok.com/concept.htm#stasis>> A fairly easy equation:> STASIS = 340 Degrees Rankine at the 0%> efficiency temperature rise.> AMBT = Ambient temperature of the panel.> OPPT = Operating temperature of the panel.> EFFICIENCY = (STASIS + AMBT - OPPT) / STASIS * 100>